Constant CONTROLS 

pub const CONTROLS: &'static AsciiSet;

Available on crate feature net only.

The set of 0x00 to 0x1F (C0 controls), and 0x7F (DEL).

Note that this includes the newline and tab characters, but not the space 0x20.

https://url.spec.whatwg.org/#c0-control-percent-encode-set